The invention relates to a drill.
Drills of the type referred to here are known. They have on their end face at least two major cutting edges which merge into minor cutting edges provided on the circumferential region of the drills. The major cutting edges are formed by faces and flanks contiguous to one another, the faces descending in the direction of rotation of the drill and the flanks descending in the opposite direction. As a rule, the drill is set in rotation and is brought into engagement with a workpiece. It is also conceivable, however, to set the workpiece in rotation and hold the drill fixedly in terms of rotation. In this case, the faces point in the opposite direction to that in which the workpiece rotates. The chips removed by the at least one major cutting edge run off on the faces. In the region of the mid-axis of the drill, a chisel cutting edge is obtained, to which the two end-face major cutting edges are contiguous. Drills of the type referred to here are usually manufactured with a relative core diameter of 10% to 35% of the drilling diameter. In the case of a core diameter greater than 20%, it is necessary to shorten the chisel cutting edge, which connects the two major cutting edges, by means by what is known as tapering out. As a result of this tapering out, center cutting edges are formed which usually form an obtuse angle with the major cutting edge. The smaller this angle is, the shorter these center cutting edges are and, as a rule, the greater the cutting efficiency which these have. The result of the tapering out is that the faces assigned to the major cutting edges form an obtuse angle with the faces assigned to the center cutting edges. In conventional ground sections of drills with a continuous flank, a greater apex angle necessarily arises in the region of the center cutting edge than in the region of the major cutting edge. It became apparent that, in such a configuration of the drill, chips removed by the cutting edges may be compacted and may not flow off freely. The drilling performance is thereby reduced. Damage to the drill may also occur.